Stringent safety requirements are imposed on adjustment drives of motor vehicle seats, since very high stresses act on the adjustment drives in the event of a collision which may result in undesired seat displacements, thus increasing the risk of injury to vehicle occupants.
To reduce the energy acting on a motor vehicle seat during a collision, it is known to provide targeted deformations of seat structures, for example by the widening of elongated holes, as described in DE 10 2007 056 373 A1.
In addition, it is known to absorb a portion of the mechanical impact energy which acts during a collision by means of elastic and/or plastic deformation of a torsion bar, thus reducing the force of the impact on a seat occupant. Such an approach is described in DE 196 48 974 A1, in which the torsion bar is arranged concentrically in a hollow shaft which connects, for example, two control arms of a seat height adjustment apparatus to one another. The hollow shaft is rigidly connected to the control arms by welding, for example, and is rotatably supported on both sides in a flange which protrudes from an upper rail of a longitudinal seat adjustment apparatus. The torsion bar is supported concentrically in the hollow shaft by two rings which are each situated in the end areas of the hollow shaft. One end of the ring is welded to the hollow shaft and to the torsion bar, while the other end of the ring is welded to the hollow shaft, but not to the torsion bar. The connection between the ring and the torsion bar is established at this end of the hollow shaft by means of a predetermined breaking point. The torsion bar is connected to a height adjustment pump at this end. During normal operation, the torsion bar transmits the torque, which acts on it from the height adjustment pump, to the hollow shaft via the rings, so that the control arms are swiveled and the seat is thus adjusted to the desired height. During a collision, the forces which act on the control arms from the seat are so large that the predetermined breaking point between the ring and the torsion bar breaks, so that the end of the torsion bar facing the height adjustment pump is no longer connected to the hollow shaft. The rigid connection to the hollow shaft is maintained at the other end of the torsion bar. The torsion bar is thus elastically and/or plastically deformed due to the forces which act on the hollow shaft from the control arms, thus reducing the momentum which acts on the vehicle seat from the collision.
A similar approach is described in WO 01/64470 A1, in which a torsion bar is concentrically arranged in a hollow shaft which connects the seat part of a vehicle seat to the seat back of the seat. A coupling nut which is coupled to the hollow shaft rests on the torsion bar in a rotationally fixed manner. The coupling nut divides the torsion bar into two sections which, at their ends, engage with bearings that are formed on the seat part. At least one of the ends of the sections is connected to its bearing in an axially fixed and rotationally fixed manner. In the event of a collision, the torsion bar deforms, so that the force which acts from the seat back is compensated for by conduction into the body. This approach makes it possible to situate the upper anchor of a seat belt on the seat back.
US 2006/0138817 A1 describes an energy absorption system for a motor vehicle seat which likewise has a torsion bar. This torsion bar extends between a first housing plate and a second housing plate, between which swivel joint fittings of the seat back and of the seat part of the motor vehicle seat are accommodated. The first housing plate and the second housing plate have elongated holes which are situated coaxially with respect to one another and which have a first end and a second end. The torsion bar is slidably situated within these elongated holes, and by means of a spring is biased toward each of the first ends of the elongated holes. When a force acts on the torsion bar in the event of a collision, the torsion bar initially moves toward each of the second ends of the elongated holes, against the force of the spring. As a result, energy which acts from the seat back is reduced in the event of a collision. When the torsion bar strikes each of the second ends of the elongated holes of the housing plates, it deforms to further absorb energy.
EP 0 806 319 B1 describes a height adjustment device of a motor vehicle seat. This height adjustment device, as is customary, has two front control arms and two rear control arms which at their respective one end are pivotably fastened to the vehicle floor or to a longitudinal seat adjustment apparatus of the motor vehicle seat, and at their respective other end are pivotably connected to the seat part of the motor vehicle seat. The drive of the height adjustment device is achieved via one of the control arms. For this purpose, this control arm has a toothed cutout with external toothing. A pinion which is driven manually or by an electric motor via a step-down gear meshes with this toothing. The seat is held in a set height position by an apparatus which blocks the rotation of the pinion. In the event of a collision, the forces which act are absorbed by the blocking apparatus of the pinion. These forces generate a torque on the pinion. To avoid a resulting unwanted rotation of the pinion, the elements which ensure the blocking of the pinion must be oversized with respect to the forces which act during normal use of the elements. This results in higher weight, greater installation space requirements, and lastly, higher costs.
To avoid these disadvantages, the approach according to EP 0 806 319 B1 is directed toward not transmitting the forces acting during the collision to the blocking apparatus of the pinion. As a result, the blocking apparatus may be dimensioned for the forces which act during normal operation of the height adjustment device. For this purpose, it is proposed to provide the driven control arm with a two-part design, with its two parts connected to one another via a predetermined breaking point and a rotational axis. Both parts have a toothed cutout with external toothing which is designed as primary toothing with which the pinion meshes. In parallel to this primary toothing and at a distance therefrom, the cutouts have secondary toothing with which the pinion does not engage during normal operation.
During normal operation, the cutouts of the two parts of the control arm are superimposed one above the other; i.e., the pinion meshes simultaneously with the primary toothing of both parts. If forces which act in the event of a collision exceed a certain threshold value, the predetermined breaking point breaks, and the two parts of the control arm may be adjusted with respect to one another about the rotational axis. Due to this adjustment, the pinion engages with the primary toothing of one part of the control arm, and engages with the secondary toothing of the other part of the control arm; i.e., the pinion is blocked against rotation due to the engagement with these two diametrically opposed toothings, so that the force absorbed by the control arm is delivered directly to the chassis via the pinion and the two parts of the control arm without a torque being transmitted to the blocking apparatus, i.e., to the drive apparatus of the pinion. This design is complicated.